The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Moving Picture Experts Group (MPEG) and Video Coding Experts Group (VCEG) have developed an improved and excellent video compression technology over existing MPEG-4 Part 2 and H.263 standards. The new standard is named H.264/AVC (Advanced Video Coding) and was released simultaneously as MPEG-4 Part 10 AVC and ITU-T Recommendation H.264. Such H.264/AVC (hereinafter referred to as ‘H.264’) uses a spatial predictive coding method, which is different from conventional video coding-related international standards such as MPEG-1, MPEG-2, MPEG-4 Part2 Visual and the like.
Conventional video coding methods use “intra prediction” for coefficients transformed in discrete cosine transform domain (or DCT transform domain) to seek higher encoding efficiency, resulting in degradation of the subjective video quality at low band transmission bit rates. However, H.264 adopts a method of encoding based on a spatial intra prediction in a spatial domain rather than in a transform domain.
An encoder using an encoding method based on the conventional spatial intra prediction predicts pixels of a block to currently encode from pixels in the previous blocks that have already undergone encoding and having been reproduced, encodes just the differences of the predicted block pixel values from pixel values of the actual block, and transmits the encoded difference information to a decoder. At this time, the encoder may either transmit parameters needed for prediction to the decoder or previously share the parameters needed for prediction with the decoder, so as to enable the decoder to predict the current block. Meanwhile, the decoder predicts information of a desired current block to be currently decoded by using information of neighbor blocks already decoded and reproduced, and reconstructs and reproduces the desired current block based on a sum of the predicted information and the difference information transmitted from the encoder. At this time also, if the decoder has received parameters need for the prediction from the encoder, the decoder uses the received parameters in predicting and decoding the current block.
However, in a prediction using the intra prediction according to the conventional video coding and video decoding, pixels of a current block to be currently encoded are predicted by referring to the already reconstructed information of adjacent pixels within a neighbor block around the current block (usually a block located at the left or above the current block). Here, the pixels of the current block to be encoded and the adjacent pixels of the neighbor block referred to in order to predict the current block may be spaced apart from each other by a considerably long distance. At this time, the accuracy of the prediction may be degraded too much, which may lower the quality of video encoding. As a result, the low quality video encoding may yield an unsatisfactory reproduction state when the image encoded with the low quality is restored and reproduced.